剑指 Offer 27. 二叉树的镜像
https://leetcode.cn/problems/er-cha-shu-de-jing-xiang-lcof/description/

struct TreeNode* mirrorTree(struct TreeNode* root){
    if(root==NULL)
    {
        return NULL;
    }

    root->left=mirrorTree(root->left);
    root->right=mirrorTree(root->right);

    struct TreeNode*tmp=root->left;
    root->left=root->right;
    root->right=tmp;

    return root;

}